Provide a hook to add an additional SSH key in the rdo-base element

Jobs ran from jenkins on ci.centos.org will start using nodepool images
but the problem is that they are set up to have the public key of the
nodepool keypair.

The nodepool private ssh key isn't going to be set up on the jenkins
nodes so let's instead add the public key of the jenkins instead.

Change-Id: Iba95d1d6818d5101c6cf02d0b9fb4cb708972957

nodepool/elements/nodepool-minimal/extra-data.d/01-nodepool-public-key

@@ -2,3 +2,5 @@
 sudo cp /var/lib/nodepool/.ssh/nodepool_rsa.pub $TMP_HOOKS_PATH/id_rsa.pub
 # Also install jenkins key
 cat /var/lib/nodepool/.ssh/jenkins_rsa.pub | sudo tee -a $TMP_HOOKS_PATH/id_rsa.pub
+# If there's an extra key, set it up too
+[[ ! -z "${NODEPOOL_SSH_KEY}" ]] && echo "${NODEPOOL_SSH_KEY}" | sudo tee -a $TMP_HOOKS_PATH/id_rsa.pub

nodepool/nodepool.yaml

@@ -12,6 +12,8 @@ diskimages:
       DIB_GRUB_TIMEOUT: '0'
       DIB_YUM_MINIMAL_CREATE_INTERFACES: '1'
       DIB_INSTALLTYPE_pip_and_virtualenv: 'package'
+      NODEPOOL_SSH_KEY: >-
+        ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAyJ4DxTKdQ8grli+FqUzoJnXWlwvhWBJwdSbKJh6en6tWwLp97dUXM2R8B5WGtggtlC7SKOSk0u49ZAOInz5lf4ljSStkWIm4DzwJWEKB5iiWgorEwhYyuKFvfikC2OMlPE8bBKCquK40gWGYeINMGeeoKWeXhB5ks4MjZqg0l65J3BGHJd4StDSd903lzNwPM9c8LBfHgEM0H7K1W/Qt86rDi2bcaDv1q1xNhVjQ8v/bR3yglnwsEjX5S6ULQlx3mYUMhfRQUiOb7bSaBlDL9faKL89GFrvkMT3zJ4v65cHpPDa3pQfuD/k+UBUhFeaXMyPFT/Wmimf2g7iLroCbhQ== rdo-ci@ci.centos.org
   - name: upstream-centos-7
     elements:
       - centos-minimal